A fuel cell is an electrochemical device for directly transforming energy of a fuel into electric energy by electrochemical reactions. It has been growingly expected as a dispersion energy source of the next generation for its high efficiency and friendliness to environments.
A fuel cell is basically composed of two separators, an electrolyte, two electrodes and two diffusion layers. The separator is generally made of a carbon-based material, because it is required to have high electron conductivity and corrosion resistance, and is provided thereon with gas flow passages formed by cutting or pressing.
When a fuel cell is of stacked structure, a through-hole referred to as manifold is provided around the separator to supply a gas to or discharge gas from each cell.
The fuel cell of the above structure tends to suffer pressure drop caused by a sudden change in passage cross-section at the connection of the manifold. Increased pressure drop in a fuel cell requires increased capacity of the blower which supplies air to the cell to increase losses at the auxiliary devices, or increased discharge pressure of the hydrogen generating unit which supplies a fuel gas to the cell, making the overall system more complex.
JP-A-2000-331691 proposes an attempt to reduce pressure drop in a cell by adopting a series of three-dimensionally curved shapes for the connection between the manifold and gas passage leading to the electrode.
However, the proposal of JP-A-2000-331691 involves a problem of increased thickness of the cell, because it three-dimensionally machines the connection between the manifold and gas passage. A fuel cell should have a stacked structure of several tens to hundreds cells to have a desired voltage, because voltage which a single cell can develop is 1V or less. Increased separator thickness increases volume and weight of the stacked cell. Therefore, the techniques for decreasing separator thickness are essential for decreased system size and cost.